[SCSI] zfcp: Remove function zfcp_reqlist_find_safe

Always use the FSF request id as a reference to the FSF request. With
this change the function zfcp_reqlist_find_safe is no longer needed
and can be removed.

Reviewed-by: Swen Schillig <swen@vnet.ibm.com>
Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>